1. Field of the Invention
The subject invention relates generally to systems designed to remove biological wastes from water reservoirs used to commercially cultivate aquatic animals. More particularly, it relates to systems which utilize a buoyant filter media to remove suspended biological matter, optimize nitrification, and to reduce biochemical oxygen demand (BOD) in large, man-made tanks used to commercially cultivate aquatic animals.
2. Description of Related Art
Commercial cultivation of aquatic animals can be a profitable business due to the existence of substantial demand for certain such animals for human consumption and enjoyment. For example, a fish suitable for commercial cultivation, known as "tilapia," has recently become increasingly popular for human consumption. The tilapia is a freshwater fish imported from Africa. Because of its foreign origin, some states prohibit introduction of the tilapia into their waterways. Consequently, fish farmers operating in these states are required to raise tilapia in man-made tanks instead of earthen ponds.
The primary disadvantage of raising fish and other aquatic animals in man-made tanks is the absence of any system for treating the biological waste generated by the fish. Without an adequate system for treating the biological wastes in the water, such wastes build-up and cause the fish to become diseased and eventually die. An adequate treatment system is especially important in the fish farming business because farm raised fish are regularly maintained in high density populations and fed frequently to increase the yield of fish, thereby increasing the amount of biological waste that must be removed to maintain a healthy fish environment.
Numerous devices have been developed to remove biological wastes from water in which fish are raised. U.S. Pat. No. 5,573,663 to Junius et al. discloses use of a floating filter media in a closed filtration tank. An auger-type mechanism is used to continuously circulate a portion of the media into a quiet zone where solids trapped in the media settle out for disposal.
U.S. Pat. No. 5,126,042 to Malone discloses another closed filter using buoyant filter media. Due to the buoyancy of the media, and the placement of the media retainer with respect to the water level in the manmade tank, the media remains packed against the upper surface of the filter even when upflowing circulation is stopped, thereby requiring a rotating blade mechanism to agitate the media for removal of solids trapped therein.
U.S. Pat. No. 4,743,382 to Williamson et al. is not specifically directed to filtration of water in which fish are raised but discloses a type of filter using a buoyant filter media. Williamson et al. discloses a system which uses buoyant filter media for removal of suspended solids remaining in the water of a clarifier tank. In Williamson et al., the water of the clarifier tank is at a higher level than the filter media and a screen retaining the media, so as to cause gravity flow from the clarifier downward through an opening in the lower part of a wall and upward through the buoyant filter media which is contained in an annular compartment surrounding the clarifier tank. Williamson et al. shows various means for cleaning portions of the filter media by circulation, water jets, or periodic blasts of gas.
None of the aforesaid patents disclose a system wherein the level of the water in the filter tank may be equalized with the level of the water in the fish tank, the water level upon equalization being below the screen retaining the filter media, thereby eliminating the tendency of the buoyant properties of the filter media to compact the media against the retaining screen prior to agitation of the media for cleaning.